The use of solid contact materials in ion selective electrode devices between an ion selective membrane and an inner reference electrode is well known and literature covering this topic is comprehensive. For example, the specifications of U.S. Pat. Nos. 2,117,596 and 3,853,731, respectively, and the specification of DE patent application No. 2220841 laid open to public inspection deal with solid contact materials. The measuring electrode devices described are disadvantageous therein that the electrochemical processes which take place in the contact material are not as effective and well-controlled as necessary to ensure stable measurement results.
Solid lithium-containing contact materials have been employed in pH electrode devices having a pH sensitive membrane of lithium containing glass. These electrode devices are disclosed in the specification of SU Pat. No. 759943 (Shul'ts) and in connection with a study concerning the stability of ion selective measuring electrode devices in Shul'ts M. M.: Journal of Applied Chemistry of the USSR, 52 (11), 2354 (1980).
Previously, intercalation electrodes have been used for other electrochemical purposes, e.g. in electrical batteries and in electrochemical measuring electrode devices of another type than the measuring electrode device according to the present invention.
The use of the materials in electrical batteries is i.a. disclosed in Whittingham M. S.: Journal of the Electrochemical Society, 123 (3), 315 (1976) and in Murphy D. W., Christian P. A.: Science 205 (4407), 651 (1971).
As far as the group of intercalation materials characterized as bronzes is concerned, the use of solid materials functioning as intercalation electrodes in measuring or reference electrode devices is i.a. disclosed in the specifications of the patents indicated below:
SU Pat. No. 834491--Dokuchaev L. Ya. et al. PA1 SU Pat. No. 785720--Volkov V. L. et al. PA1 SU Pat. No. 723447--Koksharova I. U. et al. PA1 SU Pat. No. 468893--Koksharov A. G. et al. PA1 U.S. Pat. No. 3,878,059--Wechter M. A. et al. PA1 SU Pat. No. 293493--Volkov V. L. et al. PA1 U.S. Pat. No. 3,856,634--Hahn P. B. et al. PA1 U.S. Pat. No. 3,825,482--Wechter M. A. et al. In addition to these patents further publications relating to the same topic are the following: PA1 Koksharova I. U. et al.: Issled. Stroeniya i Svoistv Oksidn. Soedin. d i f Elementov, Sverdlovsk, p. 47-49 (1980) PA1 Koksharova I. U. et al.: Akad. Nauk SSSR 31, 68-69 (1975) PA1 Koksharova I. U. et al.: Funkts. organ soedin. i polimery, p. 219-221 (1974) PA1 Koksharova I. U. et al.: Khimiya i tekhnol. vanadievykh soedin., p. 304-306 (1974) PA1 Volkov V. L. et al.: Funkts. Org. Svedin. Polim., p. 177-179 (1973) PA1 Koksharov A. G. et al.: Akad. Nauk SSSR, 25, 85-88 (1973) PA1 Hahn P. B.: Diss. Abstr. Int. B., 34(7) 3137 (1974) (Abstract) PA1 Hahn P. B. et al.: Anal. Chem., 46(4), 553 (1974) PA1 Hahn P. B.: NTIS-report No. IS-T-597 (1973) PA1 Randin J. P. et al.: J. Electrochem. Soc., 120(9), 1174 (1973) PA1 Hahn, P. B. et al.: Anal. Chem., 45(7), 1016 (1973) PA1 Wechter M. A. et al.: Anal. Chem., 45(7), 1267 (1973) PA1 Wechter M. A. et al.: Anal. Chem., 44(4), 850 (1972) PA1 Koksharov A. G.: Perm. Gos. Univ., 178 117 (1968) PA1 Koksharov A. G. et al.: Uch. Zap., Perm. Cos. Univ., 111, 63 (1964) PA1 Ibid: 178, 117 (1968) PA1 Koksharov A. G. et al.: Izv. Vyssh. Ucheb. Zaved. Khim. Khim. Tekhnol., 10, 243 (1967) PA1 the material shows ionic conductivity as far as certain ions are concerned; PA1 the material shows electronic conductivity; PA1 the crystal structure of the material provides sites into which the ions in question may enter without displacing other ions or atoms; PA1 the material is able to incorporate or give off electrons and ions of said type through a redox process which takes place internally in the material or at the surface thereof. PA1 the content of said ions may be reversibly varied in the material within certain limits by the above mentioned redox process without the formation or cleavage of any covalent bonds of appreciable strength and without any appreciable changes in the crystalline structure of the material. PA1 high ionic conductivity; PA1 high electronic conductivity; PA1 chemical resistance to water, air and a great number of chemicals; PA1 resistance to very high as well as very low temperatures; PA1 ability to bond to a glass membrane by melting or sintering; PA1 easy preparation and handling.
It is a common feature of the electrode devices disclosed in above-mentioned publications and comprising bronze intercalation compounds that they are used as reference electrodes or that the bronze intercalation compound per se is the measuring electrode, the electrode potential being determined by a redox process involving the bronze intercalation compound and the ion to be measured by the electrode device.
The above-mentioned electrode devices are rather unsuitable for pH-determination, cf. Wechter, Anal. Chem. 44 851 (1972) stating that the electrode devices disclosed are not useful in the direct determination of pH, this statement being based on comparison experiments showing a better linearity for glass electrodes than for bronze electrodes. Moreover, electrode devices based on bronze intercalation compounds as the sensitive material are unsuitable for some applications, these compounds being unstable on contact with aqueous solutions.
The use of bronze intercalation compounds intercalating the type of ions for which the activity is to be measured in ion selective electrode devices apart from pH electrodes is disclosed in the specification of DE patent application No. 2538739 laid open to public inspection. In the said specification an embodiment having a .beta.-alumina membrane between the sample and the bronze intercalation electrode has been disclosed. However, the relationship between this membrane and the selectivity of the electrode device is not clearly disclosed.
The object of the invention is to provide ion selective electrode devices which may be constructed as solid state ion selective electrode devices and which as regards the well known electrode properties such as sensitivity and stability compare to or are superior to the prior art ion selective electrode devices. In particular, the object of the invention is to provide pH measuring electrode devices.
Solid state measuring electrode devices are advantageous in many respects and for years it has been a desire to make available solid state electrode devices suited for replacing the prior art electrode devices containing an inner liquid. The solid state electrode devices may be used for a wider temperature range than the electrode devices containing a liquid; they may be arbitrarily oriented, and they are suitable for miniaturization which is of interest in connection with physiological or biochemical applications.
However, to make solid state measuring electrode devices an intersecting alternative to electrode devices containing a liquid the electrode properties should compare to those of the liquid containing electrode devices.